Friction linings are well known. Their primary purpose is to decelerate and stop a vehicle by transforming the kinetic energy of the system into heat via friction and then dissipating the heat to the surroundings. In a clutch, the primary purpose is to hold the torque put out by the engine. Other aspects of friction linings that impact overall brake performance are coefficient of friction, fade, effectiveness (braking time and speed), thermal stability and wear.
Until recently, use of asbestos in friction linings was widespread. It is well known that asbestos has many positive characteristics as a friction lining additive due to its ability to control heat, regenerate the friction surface and wear well. However, given the health hazards associated with asbestos fibers, friction material suppliers and vehicle manufacturers have shifted away from use of asbestos in friction linings. Thus, there has been a need to develop other friction lining compositions that exhibit the beneficial characteristics of asbestos, but without its use.
Generally speaking, friction linings are composites of many different materials that fulfill the functions of friction materials, abrasives, fillers, lubricants and binders. As is well known, slight changes in additive constituents and concentrations can greatly affect friction lining performance. For example, changing one additive may enhance wear but reduce braking effectiveness. Thus, an objective in developing friction lining compositions may be to find the best overall combination that achieves good performance in terms of coefficient of friction, effectiveness, fade, thermal stability and wear, depending on the specific application.